Drilling tool for laying a tube in the ground

ABSTRACT

A drilling tool for laying a tube ( 3 ) around a buried elongated element ( 1 ), comprising a drilling head ( 2 ) guided by the buried element ( 1 ), moving under the action of a pressurized fluid, from a first free end ( 14 ) of the buried element towards a second end ( 13 ) of the buried element ( 1 ), and pulling the tube ( 3 ), characterized in that the drilling tool comprises pressurization means ( 4 ) attached to the first end ( 14 ) of the buried element ( 1 ), able to slide into the tube ( 3 ) pulled by the drilling head ( 2 ) and able to create a pushing force on the drilling head ( 2 ) by the pressurization with said pressurized fluid of a pressure chamber ( 42 ) arranged between the drilling head ( 2 ) and the pressurization means ( 4 ).

The present invention relates to a drilling tool able to drill a passage around a cable or any other buried longilinear element, being guided by said cable or buried longilinear element, said tool pulling a tube behind it.

For more than a hundred years many power or telecommunication cables or other piping have been laid in the ground. Many of them are now entirely outdated from a technological standpoint or are of insufficient capacity; they should thus be replaced. Furthermore, it may be of interest to retrieve a cable which has become useless, for recuperating the copper of the conductors as well as for leaving space in the more and more encumbered subsoil.

The simplest recuperation method would consist in digging a trench over the cable to be removed. This method, expensive in itself due to civil engineering costs is highly inappropriate for work in urban areas or when the buried cable is laid next to other cables or pipes or when it crosses a pavement or a railway track.

In order to make it possible to remove a cable in such areas, various tools have been proposed. Patent No. FR 2.851.317 describes a system whereby a hoist pulls on the cable to be replaced, the end of which is connected to the new cable which is thus pulled in replacement of the old cable. Such a device requires a high power hoist the method being difficult to apply when the diameter of the replacement cable is more important than that of the cable to replace. Patent No. FR 2.492.178 describes a tool able to move along a buried cable being activated by hydraulic means, said tool providing a space around the buried cable such as to be able to remove it easily later. A new cable may then be laid in the fitted space. Document FR 2.523.170 describes an impact head able to pull a new cable.

None of the cited documents mentions a tool able to move along a cable laid in the ground and to pull a tube behind it, such as to then be able to easily remove the existent cable then lay the new cable.

To this end, the invention proposes a drilling tool for laying a tube around a buried elongated element, comprising a drilling head guided by the buried element, moving under the action of a pressurized fluid, from a first free end of the buried element towards a second end of the buried element, and pulling the tube, characterized in that the drilling tool comprises pressurization means attached to the first end of the buried element, able to slide into the tube pulled by the drilling head and able to create a pushing force on the drilling head by the pressurization with said pressurized fluid of a pressure chamber arranged between the drilling head and the pressurization means. Alternative embodiments are described in the dependent claims. The invention improves the laying of the tube around the elongated element by the creation of an additional pushing force with the pressurization of the pressure chamber.

Advantageously, the drilling head is directly fed with pressurized fluid by the pressure chamber. The present invention provides an economic tool, as the drilling head is directly fed with pressurized fluid by the pressure chamber: there are no feeding pipes which follow the drilling head during the widening of the ground around the buried cable or duct. The efficiency of the tool is also increased as there is no friction of such feeding pipes between the installed tube and the buried element.

A particular embodiment of a drilling tool according to the invention is more precisely stated in the following description, which is to be considered in connection with the accompanying drawing comprising the figures wherein:

FIG. 1. represents a general schematic view of an operation of laying a buried tube using a drilling tool according to the invention,

FIG. 2 represents a partial cross-section view of a drilling head which is part of the drilling tool according to the invention,

FIG. 3 represents a front view of a cap fixed to an end of the cable to remove and part of the drilling tool according to the invention,

FIG. 4 is a cross section view of the cap of the previous fig.,

FIG. 5 represents a front view of a safety disk, and

FIG. 6 is a lateral view of the disk of the previous figure.

FIG. 1 shows a cable 1 to remove, buried in an embankment 10, surrounded by two excavations 11 and 12 wherein the two ends 13 and 14 of the cable 1 open into. Through the excavation 12 a drilling head 2 has been introduced around the end 14, the rear side 20 of the head 2 being firmly connected to a tube 3 which thus, advances in the advancing movement of the head 2. An external drive 30, for example a caterpillar pushing drive may be provided to facilitate the advance of the tube 3. The drilling head 2 is completed with a cap 4 fixed to the rear end 14 of the cable 1. A pressurized air inlet piping 40 based on a compressor 41 is connected to the cap 4 in order to put under pressure a pressure chamber 42 arranged within the tube 3, between the cap 4 and the rear side of the tool 2. The device may be completed with a fixing disk 6 firmly fixed near to the end 13 of the cable 1 and able to press against a wall 110 of the excavation 11 in order to prevent any removal movement of the cable 1.

When the pressure chamber 42 is supplied with pressurized air by the piping 40 and through the cap 4, the latter being sealed, the air pressure rapidly increases within the chamber 42. The latter may be separated into two chambers 420 and 421 by a safety disk 5, not entirely sealed, the pressure in the two chambers 420 and 421 being equal in normal operating regime.

When the chamber 421 is put under pressure, a pushing force is exerted to the front against the rear side 20 of the drilling head. This pushing force being equal to the pressure in the chamber 421 multiplied by the section of the crown whereof the external diameter corresponds to the internal diameter of the tube 3 whereas its internal diameter corresponds to the external diameter of the cable 1. This continuous pushing force may reach values of several hundreds of daN, facilitating the progression of the drilling head 2 along the cable 1.

The drilling head 2 represented on FIG. 2 is substantially constituted of an impact head of known technique. It comprises two bodies 21 and 22 sliding onto each other by a few millimeters. The rear side 20 of the drilling head 2, respectively from the body 22 comprises one or several apertures of nozzles 200 conducting the pressurized air, coming from the chamber 421, towards a cutterhead chamber 201 provided between the bodies 21 and 22 and containing an oscillating mass 202. This chamber 201 air inlet and outlet pipes are fitted in a known manner in such a way that under the air pressure, the oscillating mass 202 starts oscillating and regularly comes to hit a rear side 210 of the body 21 of the drilling head 2, in order to make the tool 2 advance in a pulsating manner, according to a known technique of the percussion hammers. A spring means 204 is arranged in the rear portion of the cutterhead chamber 201, such as to receive and damp the shock at the rear of the oscillating mass 202. A filter, represented in 203 prevents dust or debris from penetrating into the piping 200 and blocking the cutterhead chamber 201.

The new characteristic of this drilling head 2 is found at the rear of it, where the end of the tube 3 can be seen fixed firmly to a fixing portion 220 of the body 22. This fixing portion comprises a notching or any other means making it possible to ensure a firm hold of the tube 3. A pipe clamp 221 comes to tightly encircle the end of the tube 3 by the outside in order to ensure its hold against the fixing portion 220. A seal, for example an O-ring seal 222 comes to ensure the tightness between the tube 3 and the body 22, thus creating the pressurizing chamber 421, thus enabling a continuous additional push such as described previously coming to be added to the penetration force by percussion described above.

FIGS. 3 and 4 are two representations of the previously mentioned cap 4. Such as represented, the cap 4 is in its normal operating state, the pressurized air inlet piping 40 being connected to a piping fixing represented in 400. A pipe 401 arranged coaxially to the cap 4 and crossing it on either side opens onto apertures 402 supplying the chamber 42, respectively 420, with pressurized air. A fastener 43 connects a cylindrical portion 430 of the cap 4 to an attaching means 15 fixed to the end of the cable 1. A sealing means 44 for example an O-ring seal, ensures tightness between the chamber 420 and the rear portion of the tube 3. This sealing means 44 is a means allowing for the sliding of the tube 3 around the cap 4 during the pulling of the tube 3 by the drilling head 2.

When the drilling head 2 has advanced by a few dozen meters along the cable 1, the pressurized air in the chamber represents a very high power. In the case where the attachment means 43, 15 break between the cable 1 and the cap 4, the latter would thus be hurled along the rear end of the tube 3 such a cannonball. The staff at work in the excavation 12 may thus be subjected to severe harm.

In case of rupture of the attachment means 43, 15 between the cap 4 and the cable 1, the cylindrical portion 430 is not retained anymore by the cable 1, the air pressure in the chamber 42 may thus push to the right of the fig., via apertures 431, a tapered cone crown 432 fixed to said cylindrical portion 430. By this axial movement, two brake linings 433, able to be moved radially, are pushed outwards by their tapered contact surfaces and come to brake then block the cap 4 against the internal surface of the tube 3. Simultaneously, the pressurized air supply apertures 402 of the chamber 42 close up by sliding the tubular portion 430, thus cutting the pressurized air supply of this chamber.

The cap 4 thus substantially serves to create the pressure chamber 42, this cap 4 being provided with safety means described to prevent any accidents if its attachment means happen to break.

An additional means may still be provided in order to prevent the consequences of a malfunctioning of the device. This means is constituted of a safety disk, represented in 5 on FIG. 1. As represented on FIGS. 5 and 6, the safety disk 5 is constituted of two semi-tubular portions 50 and 51, tightly encircling a portion close to the rear end of the cable 1 and fixed together with screws 52. As indicated compared with FIG. 1, this disk 5 separates the pressure chamber 42 into two portions 420 and 421. These portions are not sealingly separated, there are links between these portions on the border of the disk 442 as well as between the two semi-tubular portions 423. In normal operation, the air pressure may easily pass from the chamber 420 to the chamber 421 by links 422 and 423, whereas in the case of sudden depression in the chamber 420, the air of the chamber 421 will only escape more slowly.

The device may be completed with a fixing disk represented in 6 on FIG. 1. It is a disk of external diameter clearly larger than that of cable 1 and fixed firmly on it at its end 13 opening into the excavation 11. When the drilling head 2 reaches the vicinity of the excavation 11, the remaining portion of the cable 1 between the drilling head 2 and the wall 110 of the excavation 11 may be too small to retain the cable 1, the latter thus being able to be swallowed by the drilling head 2. In order to prevent this, the fixing disk 6 thus abuts against the wall 110, preventing the movement of the cable 1 into the ground.

The above mentioned specification describes a preferred embodiment of a drilling tool according to the invention; it is obvious that various constructive alternatives of one or the other of the described elements may be considered.

Particularly, the tool has been described to operate with pressurized air, an equivalent tool may also operate with a liquid, for example pressurized water, the skilled person being able to adapt the described elements to such functioning.

The tool according to the invention has been described as adaptable to the retraction of a cable 1; it is obvious that it may easily adapt itself to the retraction of a piping or any other longilinear or elongated element of circular section. 

1. A drilling tool for laying a tube around a buried elongated element, comprising a drilling head guided by the buried element, moving under action of a pressurized fluid, from a first free end of the buried element towards a second end of the buried element, and pulling the tube; and pressurization means attached to the first end of the buried element, able to slide into the tube pulled by the drilling head and able to create a pushing force on the drilling head by the pressurization with said pressurized fluid of a pressure chamber arranged between the drilling head and the pressurization means.
 2. The drilling tool according to claim 1, wherein the drilling head is directly fed with pressurized fluid by the pressure chamber.
 3. The drilling tool according to claim 1, further comprising: on a front portion, the drilling head comprising a first impact body sliding over a second concentric body, an oscillating mass activated by means for supplying and channeling the pressurized fluid regularly coming to hit a rear side of said impact body, said drilling head operating like a percussion hammer, the drilling head being arranged and advancing coaxially to the buried elongated element, wherein the second concentric body comprises sealing fixing means of said tube, and wherein the pressurization means are a cap with a cylindrical shape, arranged behind the drilling tool and behind the first free end of the elongated element, within the tube during the pulling, said cap being attached to said free end and being provided with sliding sealing means between its perimeter and the internal surface of the tube, said cap comprising attachment means of a feeding pipe with the pressurized fluid, a feeding pipe feeding with said pressurized fluid inside the pressure chamber arranged in the front portion of the tube, between a rear side of the second body and a front side of said cap, the pressure exerted by said pressurized fluid creating the substantially continuous pushing force against the rear side of the second body contributing to the pushing of said drilling head pulling the tube around the elongated element.
 4. The drilling tool according to claim 3, wherein the sealing fixing means of the tube on the second concentric body comprise a substantially cylindrical portion of the second concentric body with notches as well as an O-ring seal arranged between said second concentric body and the tube.
 5. The drilling tool according to claim 4, wherein the sealing fixing means of the tube on the second concentric body further comprise a pipe clamp arranged on the outside surface of the tube and coming to press said tube against the substantially cylindrical surface of the second concentric body provided with notches.
 6. The drilling tool according to claim 3, further comprising filter means for filtering fluid in the pipes of the fluid system.
 7. The drilling tool according to claim 1, wherein said substantially continuous pushing force applied to the drilling head is substantially equal to the product of the fluid pressure value in the pressure chamber multiplied by the section of the crown whereof the external diameter equals the internal diameter of the tube and the internal diameter equals the external diameter of the elongated element.
 8. The drilling tool according to claim 1, wherein the associated pressurization means comprise a safety means comprising at least two brake linings able, during a rupture of the attachment of the pressurization means to the end of the elongated element, to move radially and to block the pressurization means within the tube, under the action of a conical crown activated by the pressure inside the pressure chamber, a means further being provided to cut the arrival of the pressurized fluid in the pressure chamber.
 9. The drilling tool according to claim 1, further comprising a safety disk comprising two semi-tubular portions tightly encircling a portion close to the first rear end of the elongated element and fixed together by screws, said safety disk separating the pressure chamber into two portions of chambers, a fluid communication of small section being provided in the safety disk and connecting the two portions of chambers.
 10. The drilling tool according to claim 1, wherein the fluid is air.
 11. The drilling tool according to claim 1, wherein the fluid is a liquid.
 12. The drilling tool according to claim 1, further comprising a fixing disk attached to the elongated element close to the second free end of said elongated element, a supporting surface of said disk coming to abut against a wall of backfill in order to prevent a retraction movement of the elongated element.
 13. The drilling tool according to claim 1, wherein the elongated element is an electric power or telecommunications cable.
 14. The drilling tool according to claim 1, wherein the elongated element is a pipe.
 15. A method for laying a tube around a buried elongated element comprising: causing the advance of a drilling head by means of a pressurized fluid, from a first free end of the elongated element; pulling the tube by the drilling head; creating a pressure chamber between the drilling head and the first free end of the elongated element; and applying an additional pushing force on the drilling head by pressurizing the pressure chamber. 